Chemical waste and scrap material is of increasing concern to society, and as a result, the chemical industry is increasingly focusing its attention on the recycling and re-using of chemical materials.
Silicones, otherwise known as organosiloxanes, are polymeric materials having alternate silicon and oxygen atoms with various organic radicals attached to the silicon. These compositions can be liquid, semisolid or solid, depending upon the molecular weight and degree of crosslinking. Such polymers may be chain extended and/or crosslinked chemically, with or without catalyst.
Silicones are generally stable over temperature ranges from about -50.degree. to about +250 .degree. C. and sold in the form of fluids, powers, emulsions, solutions resins, pastes, elastomers and the like. Liquid silicones are used in adhesives, sealants, lubricants, protective coatings, coolants, mold-release agents, dielectric fluids, heat transfer, wetting agents and surfactant, foam stabilizer for polyurethanes, diffusion pumps, antifoaming agent for liquids, textile finishes, water repellents, weatherproofing concrete, brake fluids, cosmetic items, polishes, foam shields for solar energy collectors and rust preventives. Silicone resins are used in coatings, molding compounds, laminates (with glass cloth), filament winding materials, room temperature curing cements, electrical insulation, impregnating electric coils, bonding agents, modifiers for alkyd resins, and vibration damping devices. Elastomer or silicone rubber is used in encapsulation of electronic parts, electrical insulation, gaskets, surgical membranes and implants automobile engine components, flexible windows for face masks, sealants, air locks and the like.
Once used, silicones generally cannot be melted down and reused. Once crosslinked, molded or reacted, any scrap must generally be discarded.
U.K patent 2,015,550 to Heidingfeldova, et al., is directed to a method of reclaiming siloxanes by dissolving the siloxane in an amine. However, amines produce noxious odors and the overall process is rather inefficient.
U.S. Pat. No. 3,989,733 to Okamotoa, et al., is directed to a process for the preparation of cyclic polydiorganosiloxanes by a complex distillation process having a vertical packed catalysts zone with an inlet stream at about the middle of the catalyst zone. The process is run at a pot temperature in excess of about 240.degree. C. and is a fix bed, base catalyzed reaction.
U.S. Pat. No. 3,714,213 to Ryan is directed to a method for making cyclopolysiloxanes by cracking the poly(siloxanes) over acid-treated clay or synthetic aluminum silicate. A drawback to this method is that it must be conducted at extreme temperatures.
In Chemistry of Materials, Vol. 1, 445-451, 1989, "Synthesis of Cyclic Siloxanes by the Thermal Depolymerization of Linear Poly(siloxanes)" is directed to a fixed bed, acid catalyzed distillation process run at temperatures of from about 500.degree. C. to about 700.degree. C.
As exemplified by the above references, the thermal depolymerization of linear poly(siloxanes) has generally been achieved by either an acid catalyzed cracking reaction or a base catalyzed cracking reaction, typically in combination with temperatures in excess of 180.degree. C. Cracking reactions less than about 180.degree. C. have been achieved by use of an amine solvent, but such processes have proven to be inefficient and have a tendency to produce noxious odors.
It is therefore and object of the present invention to provide a process for recycling silicone materials which is efficient, which can be accomplished at temperatures less than about 180.degree. C., which does not have a tendency to produce noxious odors and which is sufficiently economical to justify full scale commercialization. Other objects and features of the present invention will become apparent to those of ordinary skill in the art upon a further reading of this specification and accompanying claims.